Computer Audio via USB and Jitter?

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watersb

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Computer Audio via USB and Jitter?
« on: 28 Aug 2005, 11:21 pm »
My first post!  :)

I just read a wonderful article in (next month's?) Stereophile magazine, regarding the Wavelength Audio USB DAC:

Quote

[Wavelength Audio designer Gordon Rankin:] "Most of these things go from the USB connection standard to an S/PDIF environment, and then to an input receiver, but I didn't want to do that. I designed my converter to go straight from the USB connection to the Philips TDA1543 chip"...

Any D/A converter and its datastream source must be synchronized with one another, and in a system of digital separates, that's usually accomplished by having the converter lock on to the word-clock signal contained in the datastream from the transport. According to Rankin, the S/PDIF environment is more prone to unwanted variations in the frequency of the incoming word-clock signal, which the converter is always trying to track. But with a USB controller generating its own word-clock signal, the frequency remains steady. "In USB," Rankin says, "the bit clock and the word clock are almost a given: There are only a few frequencies it has to deal with, and if it sees a standard PCM signal coming in ... it doesn't waver."


The interesting point here is that, properly constructed, a USB DAC hooked up to a computer should not have the timing issues that (ostensibly) motivate the expense of a high-end digital transport/outboard DAC combo.

I gather this is a controversial issue.

I've ordered my modded Teac with a USB Select jammed into it... this should be an awesome match to my Mac Mini "transport".

But do Gordon Rankin's comments apply to any USB audio interface? I gather not, as people seemed concerned about jitter in their outboard USB DACs... how much of a problem is this, really, with USB audio (and in contrast to S/PDIF coax connection)?

watersb

  • Jr. Member
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Computer Audio via USB and Jitter?
« Reply #1 on: 31 Aug 2005, 04:13 am »
OK, I found this thread.. and many others.. on AudioAsylum:

http://64.154.92.195/scripts/t.pl?f=pcaudio&m=620

Vinnie R.

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Computer Audio via USB and Jitter?
« Reply #2 on: 31 Aug 2005, 11:09 am »
Quote from: watersb
OK, I found this thread.. and many others.. on AudioAsylum:

http://64.154.92.195/scripts/t.pl?f=pcaudio&m=620


Hi watersb,

Welcome to the Red Wine Circle, and thanks for your post and provided link!  

Quote from: watersb
But do Gordon Rankin's comments apply to any USB audio interface? I gather not, as people seemed concerned about jitter in their outboard USB DACs... how much of a problem is this, really, with USB audio (and in contrast to S/PDIF coax connection)?


I'd say Rankin's comments don't apply to any USB audio inteface...it really depends on implementation.  There are plenty of variables, and as I and many others believe, a component that measures better doesn't always sound better.  :wink:

Regards,

watersb

  • Jr. Member
  • Posts: 17
Computer Audio via USB and Jitter?
« Reply #3 on: 31 Aug 2005, 02:40 pm »
Thanks Vinnie!

http://www.audioasylum.com/forums/pcaudio/messages/578.html
Quote

A really good thing to try would be a USB DAC using the 1020 in async mode, programmed so it provides this other interface and feed it to one of these new DACs in filterless mode, then use a transformer output stage which does a good job of the remaining filtering necessary. I think this would be a really exceptional device.


So MY big question(s) is, what mode does the M-Audio Transit drive the TAS1020?

What's the best USB DAC to use? Does the USB Select address these issues?

How about modding some other USB DAC?


(From what I've read so far, no consumer-affordable device, USB or otherwise, can beat a modded SqueezeBox 2... there are some relatively-expensive digital components in there, the Xilinx FPGA, Burr-Brown DAC... to say nothing of the VHDL programming expense! They could not afford to take the guy-in-the-garage approach to this, I'm glad the device is popular enough to keep the price low.)